Ti2Al(O,N) formation by solid-state reaction between substoichiometric TiN thin films and Al2O3 (0001) substrates

Titanium nitride TiNx (0.1 ≤ x ≤ 1) thin films were deposited onto Al2O3(0001) substrates using reactive magnetron sputtering at substrate temperatures (Ts) ranging from 800 to 1000 °C and N2 partial pressures (pN2) between 13.3 and 133 mPa. It is found that Al and O from the substrates diffuse into the substoichiometric TiNx films during deposition. Solid-state reactions between the film and substrate result in the formation of Ti2O and Ti3Al domains at low N2 partial pressures, while for increasing pN2, the Ti2AlN MAX phase nucleates and grows together with TiNx. Depositions at increasingly stoichiometric conditions result in a decreasing incorporation of substrate species into the growing film. Eventually, a stoichiometric deposition gives a stable TiN(111) || Al2O3(0001) structure without the incorporation of substrate species. Growth at Ts 1000 °C yields Ti2AlN(0001), leading to a reduced incorporation of substrate species compared to films grown at 900 °C, which contain also Ti2AlN(101̅3) grains. Finally, the Ti2AlN domains incorporate O, likely on the N site, such that a MAX phase oxynitride Ti2Al(O,N) is formed. The results were obtained by a combination of structural methods, including X-ray diffraction and (scanning) transmission electron microscopy, together with spectroscopy methods, which comprise elastic recoil detection analysis, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy.